How to parse HTML using PHP?

Question

Possible duplicate:
How to parse and process HTML using PHP?

Suggestion for reference . There are dozens of "How to parse HTML" questions that appear every day. However, it is very difficult to close as a duplicate, because most of the questions relate to the specific scenario presented by the appellant. This question is an attempt to build a general "reference question" that covers all aspects of the problem.

This is an experiment. If such a reference question already exists, let me know and I will gladly delete this one.

My ideal vision is that each of the three questions gets an answer separately, and the best answers for each bubble up.

I will award 200 bounties with the best answer in each of the three categories in two weeks, pending discussion of this issue on Meta strong>.

Each of these questions has already received a brilliant answer elsewhere, so copying + pasting my own answer to another question is fine with me.

How to parse HTML using PHP?

• What libraries exist? Which ones use the PHP DOM, which have their own parsing engine? (Hint: SimpleHTMLDOM)

  1a. I need to find a specific item, but it's hard for me to get used to the XPath syntax. Are there any DOM-based libraries that simplify HTML parsing? Please consider creating common examples in the real world.

• Is there a PHP library that allows me to query the DOM using CSS [2/3] selectors like jQuery? (Hint: phpQuery). Please consider creating common examples in the real world.

• Bonus question: why shouldn't I use regular expressions? Please provide a very short answer in layman's terms.